Generally, a half bridge circuit is provided to drive an inductive load. Inductive loads that require supplied current include motors, coils, valves, and the like. Certain DC converters and switching rectifier topology circuits are also driven by a half bridge. The half bridge circuit provides a high side driver, typically a MOS driver transistor, coupled between a supply and a load output and having a high side gating control signal. The half bridge also provides a low side driver, also typically a MOS driver transistor, coupled between the load output and a ground terminal and having a low side gating control signal. In most applications, a time varying input signal is provided, which is a switching signal. In some applications, this signal may be a pulse width modulated but fixed frequency switching signal. In other applications, this input signal may be a pulse frequency modulated input signal that has a variable frequency and a constant or variable duty cycle. In any case, as the load requires current, switching signals at the input are used to determine the gating signals needed at the high and low side drivers. Because the load is inductive, the switches must also provide a discharge current path from the inductor when the high side driver is switched off. Also, a “dead time” is needed between cycles so that the low and high side driver are never both active, as that creates a “shoot through” current path through the driver transistors from the supply voltage to ground, creating inefficiency and power loss.
In order to achieve proper current regulation in the inductive load, it is necessary to switch between the high side driver “on” and the low side driver “on”. The requirement that a “dead time” be maintained between the high side driver on and the low side driver on cycles places a limit on the switching speed of the circuit. Further, the circuitry used to create the “dead time” is unreliable and may, in certain circumstances, allow the “shoot through” current to occur, even if the circuitry was designed not to do so.
A continuing need thus exists for an efficient and reliable circuit and methods to control the switching operations of a half bridge circuit driving an inductive load.